Effect of Electrode Type on Bacteria Removal and Chlorine and Radical Production in Electrochemical Water Disinfection
At a Glance
Section titled âAt a Glanceâ| Metadata | Details |
|---|---|
| Publication Date | 2021-09-15 |
| Journal | Deu Muhendislik Fakultesi Fen ve Muhendislik |
| Authors | Emine Esra Gerek, AyĆe Tansu Koparal, Ali SavaĆ Koparal |
| Institutions | Eskisehir Technical University, Anadolu University |
| Analysis | Full AI Review Included |
Executive Summary
Section titled âExecutive SummaryâThis research evaluates the comparative performance of three electrode typesâBoron-doped diamond (BDD), Iridium metal-oxide (IrOx), and Graphite plate (GP)âfor electrochemical disinfection of E. coli-contaminated groundwater.
- Core Objective: To identify the optimal electrode material that achieves high bacterial elimination while minimizing the production of toxic disinfection by-products (excess chlorine and total oxidizers).
- Performance Ranking (Disinfection): IrOx electrodes showed the fastest bacterial killing, followed closely by BDD, with Graphite plates being the least effective, particularly at lower current densities.
- By-Product Ranking (Toxicity): IrOx generated the highest concentrations of excess chlorine (4.2 mg/L) and total oxidizers (90 mg/L H2O2 equivalent) under continuous flow conditions.
- BDD Compromise: BDD electrodes achieved disinfection levels comparable to IrOx, yet produced significantly lower levels of excess oxidants, making them the preferred choice for sensitive applications.
- Process Optimization: Higher flow rates (150 ml/min) consistently improved disinfection efficiency across all electrode types due to enhanced mass transfer and increased turbulence, facilitating faster chemical dispersion.
- Conclusion: BDD electrodes offer the best compromise, providing aggressive disinfection capability while maintaining low residual oxidant levels, suitable for drinking water or discharge into aquatic environments.
Technical Specifications
Section titled âTechnical SpecificationsâThe following table summarizes the key operational parameters and comparative performance metrics derived from the continuous flow experiments (30 mA/cm2 current density, 150 ml/min flow rate).
| Parameter | Value | Unit | Context |
|---|---|---|---|
| Electrode Materials Tested | BDD, IrOx, Graphite Plate | N/A | Parallel plate reactor configuration |
| Initial Bacterial Load | ~105 | CFU/mL | E. coli (ATCC 25922) in real groundwater |
| Current Density Range | 10, 20, 30 | mA/cm2 | Applied DC electricity |
| Flow Rate Range | 50, 100, 150 | ml/min | Tested in both recursive and continuous modes |
| Groundwater pH | 7.8 | N/A | Stable range during all experiments (7.2 to 7.4) |
| Groundwater Conductivity | 700-900 | ”s/cm | Real sample range |
| BDD Chlorine Concentration | 0.833 | mg/L | Continuous flow output (30 mA/cm2) |
| IrOx Chlorine Concentration | 4.2 | mg/L | Continuous flow output (5x higher than BDD) |
| Graphite Chlorine Concentration | 0.173 | mg/L | Continuous flow output (Lowest chlorine production) |
| BDD Total Oxidizer (H2O2 equiv.) | 30 | mg/L | Continuous flow output (30 mA/cm2) |
| IrOx Total Oxidizer (H2O2 equiv.) | 90 | mg/L | Continuous flow output (Highest radical production) |
| Graphite Total Oxidizer (H2O2 equiv.) | 130 | mg/L | Continuous flow output (Note: High H2O2 equiv. despite low chlorine) |
| BDD Residual Bacteria | 5 | CFU/mL | Continuous flow after disinfection |
| IrOx Residual Bacteria | 1 | CFU/mL | Continuous flow after disinfection (Fastest elimination) |
Key Methodologies
Section titled âKey MethodologiesâThe electrochemical disinfection process was studied using a controlled, comparative approach focusing on electrode material and electrical parameters.
- Water Sample Preparation: Real groundwater samples were sourced from EskiĆehir (Muttalip suburb) and inoculated with E. coli (ATCC 25922) to simulate contamination, achieving an initial concentration of approximately 105 CFU/mL.
- Reactor Configuration: A parallel plate reactor setup was utilized, where both the anode and cathode were constructed from the same material (BDD, IrOx, or Graphite plate, 4.5 cm x 3.1 cm).
- Electrolysis Modes: Experiments were conducted in two operational modes:
- Recursive System: Water was recirculated back to the solution tank for batch treatment.
- Continuous Flow System: Water was passed through the reactor and collected as output.
- Parameter Variation: Three current densities (10, 20, and 30 mA/cm2) and three flow rates (50, 100, and 150 ml/min) were systematically tested for each electrode type.
- Bacterial Viability Assessment: The number of surviving bacteria was determined using the standard plaque counting method. Samples were collected at 2-minute intervals and neutralized with sodium thiosulfate before plating on Nutrient agar.
- Chlorine Quantification: Total chlorine concentration was measured spectrophotometrically using the Diethyl-p-phenylenediamine (DPD) method (Lange-Hach kits).
- Total Oxidizer Quantification: Total oxidizer production (including radicals) was measured spectrophotometrically at 352 nm and expressed as hydrogen peroxide (H2O2) equivalent.
Commercial Applications
Section titled âCommercial ApplicationsâThe findings support the deployment of electrochemical disinfection systems, particularly those utilizing Boron-doped diamond (BDD) electrodes, in applications requiring high disinfection efficacy with strict control over residual toxic by-products.
- Decentralized Water Treatment: Ideal for small-scale or remote groundwater treatment systems where chemical storage and transport are impractical, leveraging the in situ generation of disinfectants.
- Drinking Water Purification: BDD electrodes provide the necessary microbial kill rate while minimizing residual chlorine and radicals, addressing health concerns associated with trihalomethane formation.
- Sensitive Aquatic Discharge: Applicable in industrial or municipal wastewater treatment where effluent is discharged into lakes or rivers, as the low radical output of BDD minimizes toxicity to aquatic life.
- Point-of-Entry/Point-of-Use Systems: Suitable for residential or commercial buildings requiring reliable, automated disinfection without the need for continuous chemical dosing.
- Advanced Oxidation Processes (AOPs): BDD electrodes are highly effective for generating hydroxyl radicals (OH), making them valuable in AOPs for degrading persistent organic pollutants alongside disinfection.
View Original Abstract
Formation and contamination of malicious microorganisms and viruses remain to be major problem of water resources. This is mostly due to the fact that, groundwater, which constitutes a large share of available fresh water content, is prone to contamination from urban and industrial wastes. In this work, electrochemical treatment is considered as a disinfection mechanism. The literature presents several cases of individual of electrochemical disinfection experiments. In this particular work, we aim to focus on the comparative disinfection efficiency of Boron-doped diamond electrodes, Iridium metal-oxide electrodes and Graphite plate electrodes at various electrochemical settings, whilst monitoring formation of toxic bi-products, such as chlorine and other radicals. Experiments of electrochemical water disinfection were carried out on real groundwater samples deliberately contaminated with E. coli culture. During the reaction, microorganisms die due to both direct physical damage and due to the electrochemically generated radicals. Therefore, there is a gentle balance of bacteria elimination versus avoiding excessive radical production in the treated water. Since the biological behaviour of the microorganisms and the chemical properties of the available groundwater cannot be changed, the research parameters boil down to experimenting through various popular electrode types and electrical current settings. In both continuous-flow and recursive systems, the Boron-doped diamond electrodes are observed to provide desirable level of disinfection (as good as Iridium metal-oxide), while yielding lower radicals (as low as those of Graphite-plate), making an ideal compromise for the process.